1. Field of the Invention
This invention relates to an anti-skid device for automobile tires.
2. Description of the Prior Art
The conventional anti-skid devices for automobile tires which have mainly been used are the anti-skid devices disclosed in Japanese Patent Publication Nos. 13337/1983 and 49366/1983. In these examples, an inner rope C is fixed via inner metal members G or directly to the inner side surface of a tire skid preventing net body B as shown in FIG. 14, and the tire skid preventing net body B is put over a tire T with the inner rope C fixed to the tread thereof. Both ends of this net body B are then joined together by a suitable method so that the net body B extends annularly. The inner side surface portion of the net body B is then tightened with the rope C, and the outer side surface portion thereof with a setting strap D via outer metal members E to set the anti-skid device as shown in FIG. 15.
However, according to this method, hooking the setting strap D on a plurality of outer metal members E one by one takes much time and labor.
This setting strap D in use is designed so that it can be handled without much pulling force, taking a female user into consideration. Another reason why the setting strap D is made in the mentioned manner resides in that, if the strength of the setting strap D is set excessively high, the rope C used on the inner side surface of the net body B would be broken. It has been considered impossible for this reason as well that the strength of the setting strap D be set excessively high. Therefore, when a centrifugal force is applied to the tire skid preventing net body B while the vehicle travels, the setting strap D expands to cause the net body B to be lifted and slipped on the tire T. Consequently, the net body B becomes rather loose with respect to the tire T, and variation of position of the net body and a locally concentrated load occur to cause the net body B to be locally broken or displaced, making such an anti-skid device unfit for use.
Especially, in the case of a non-metallic net type anti-skid device which is in recent years growing to be a leading anti-skid device of this kind, the slipping of a tire skid preventing net body B due to a centrifugal force from the tire T causes a decrease in the durability of the device, and the upward movement of the net body B which brings the net body B into contact with the inner surface of the fender and results in the breakage of the net body B. These inconveniences suggest the important points of designing the anti-skid device. On the other hand, it is necessary that the level of the tightening force occurring in the setting strap D as a whole for the prevention of the slipping of the net body B be increased. Under the circumstances, there is a limit to the tension of the setting strap D which can be hooked manually with ease on the outer metal members E, and the tension of such a single setting strap D cannot prevent the slipping of the tire skid preventing net body B from the tire T which occurs due to the centrifugal force exerted on the net body B when the tire T is rotated.
Therefore, two to three pieces of setting straps the tension of which is set to the very limit of the range of levels at which the setting straps D can be hooked manually on the outer metal members are generally used. Since the operation of hooking the increased number of setting straps D one by one on each of a plurality of outer metal members E sequentially causes an increase in the length of time and quantity of labor for carrying out the attaching and detaching of the anti-skid device to and from a tire, it hinders the further popularization of this kind of anti-skid device which has been reconsidered in view of the prospective total abolition of spike tires.
The conventional tire skid preventing net body B shown in FIG. 15 is formed flat as shown in FIG. 14, and the tightening portions thereof which are to be applied to the inner side surface of a tire T are then set to a pitch lu' at which these tightening portions are held finally on the tire by using inner metal members G. Regarding the tightening portions of the net body B which are to be applied to the outer side surface of the tire T, the diameter of a circle connecting these tightening portions held on the outer side surface of the tire T by hooking the setting strap D on the outer metal members E and tightening the same is reduced so that the pitch lo of these tightening portions of the net body B in a flat-extending state becomes lo'.
Unless a sufficiently large pitch of the tightening portions of the tire skid preventing net body B which correspond to the outer side surface of a tire is secured, the net body B cannot be set on the tire. Therefore, the net body B is set on the tire T with the outer tightening portions spaced with the same pitch lo as that when the tightening portions of the net body B is laid in a flat-extending state. Thus, a lot of energy is required to reduce the pitch of the tightening portions corresponding to the outer side of the tire to the level at which these tightening portions are finally held on the tire, and putting the net body over the tire and fixing the same thereto in this manner also causes the tightening portions to be swollen greatly by the centrifugal force.